In general, an auto-focus or zoom lens module used in a digital camera usually comes with a very limited space, and the module must comply with the requirements for a light, thin, short and compact design as well as high precision and durability. Most of the conventional auto-focus or zoom lens modules use the electromagnetic force of a voice coil motor (VCM), a piezoelectric motor, or a solenoid to drive a lens module. As disclosed in U.S. Pat. Nos. 7,295,388, 6,654,185 and 7,298,562, a plurality of electromagnets are used to control the movement of a camera lens in different directions; or as disclosed in U.S. Pat. Application Nos. 2007/0097532, 2004/0130808, the direction of current inputted to the solenoid is controlled to generate different magnetic fields by the solenoid generates and produce attractions or repulsions by magnetic elements mounted on a camera casing to move the camera lens; or as disclosed in U.S. Pat. No. 7,262,927, U.S. Pat. No. 7,196,978, U.S. Pat. No. 7,002,879, U.S. Pat. No. 6,961,090, U.S. Pat. No. 6,687,062, US2007/0133110, Japan Pat. No. JP2005-037865, JP2005-258355, WO2007/026830, a solenoid, magnet and a resilient element (such as a spring or a resilient plate) of a voice coil motor (VCM) are used for the movement of the camera lens, or as disclosed in U.S. Pat. No. US2007/0146894, U.S. Pat. No. 7,212,358, US2003/0227560, Japan Pat. No. JP2006-293083, JP2006-101611, a piezoelectric motor made of a piezoelectric material is used for controlling the movement of the camera lens.
In FIG. 1, four permanent magnets 103˜106 are mounted on the frame 100 of the conventional lens module to produce a magnetic field, and a barrel 107 is mounted onto the frame 100, and the lens 101 is coupled at the solenoid 102 and disposed in the barrel 107. After the solenoid 102 is conducted electrically to produce a magnetic field, the direction of the magnetic field produced by four permanent magnets 103˜106 and upward or downward electromagnetic forces formed by magnetic poles are used for driving the camera lens to move. However, the permanent magnets 103˜106 will be demagnetized by the high temperature of a reflow process (around 260° C. in reflow oven), and thus reflow process cannot be used for the manufacture of a lens driving apparatus that adopts the aforementioned conventional methods that use an electromagnetic force of a solenoid and a driving device of a permanent magnet, and thus the mass production efficiency will be restricted.
Further, a lens moving mechanism adopting a shaped memory alloy (SMA) is used, and the characteristics of thermal contractions and expansions of the SMA are used as the driving force source of an actuator as disclosed in U.S. Pat. Nos. 6,307,678, 6,449,434, 2007/0058070 and 2007/0047938 and Japan Pat. No. 2005-275270 and 2005-195998, but the thermal contraction and expansion of the SMA are relatively slow, and an instant auto-focus or zooming effect cannot be achieved easily.
In view of the foregoing shortcomings of the prior art, the inventor of the present invention based on years of experience in the related industry to conduct extensive researches and experiments, and finally developed an apparatus of driving a lens by an electromagnetic driving force in accordance with the present invention to overcome the shortcomings of the prior art.